Page:EB1911 - Volume 10.djvu/42

Rh hypothesis of monads, and by Nicholas Malebranche; while, in the middle of the 18th century, not only speculative considerations, but a great number of new and interesting observations on the phenomena of generation, led the ingenious Charles Bonnet and A. von Haller, the first physiologist of the age, to adopt, advocate and extend them.

Bonnet affirms that, before fecundation, the hen’s egg contains an excessively minute but complete chick; and that fecundation and incubation simply cause this germ to absorb nutritious matters, which are deposited in the interstices of the elementary structures of which the miniature chick, or germ, is made up. The consequence of this intussusceptive growth is the “development” or “evolution” of the germ into the visible bird. Thus an organized individual (tout organisé) “is a composite body consisting of the original, or elementary, parts and of the matters which have been associated with them by the aid of nutrition”; so that, if these matters could be extracted from the individual (tout), it would, so to speak, become concentrated in a point, and would thus be restored to its primitive condition of a germ; “just as, by extracting from a bone the calcareous substance which is the source of its hardness, it is reduced to its primitive state of gristle or membrane.”

“Evolution” and “development” are, for Bonnet, synonymous terms; and since by “evolution” he means simply the expansion of that which was invisible into visibility, he was naturally led to the conclusion, at which Leibnitz had arrived by a different line of reasoning, that no such thing as generation, in the proper sense of the word exists in nature. The growth of an organic being is simply a process of enlargement, as a particle of dry gelatine may be swelled up by the intussusception of water; its death is a shrinkage, such as the swelled jelly might undergo on desiccation. Nothing really new is produced in the living world, but the germs which develop have existed since the beginning of things; and nothing really dies, but, when what we call death takes place, the living thing shrinks back into its germ state.

The two parts of Bonnet’s hypothesis, namely, the doctrine that all living things proceed from pre-existing germs, and that these contain, one enclosed within the other, the germs of all future living things, which is the hypothesis of “emboîtement,” and the doctrine that every germ contains in miniature all the organs of the adult, which is the hypothesis of evolution or development, in the primary senses of these words, must be carefully distinguished. In fact, while holding firmly by the former, Bonnet more or less modified the latter in his later writings, and, at length, he admits that a “germ” need not be an actual miniature of the organism, but that it may be merely an “original preformation” capable of producing the latter.

But, thus defined, the germ is neither more nor less than the “particula genitalis” of Aristotle, or the “primordium vegetale” or “ovum” of Harvey; and the “evolution” of such a germ would not be distinguishable from “epigenesis.”

Supported by the great authority of Haller, the doctrine of evolution, or development, prevailed throughout the whole of the 18th century, and Cuvier appears to have substantially adopted Bonnet’s later views, though probably he would not have gone all lengths in the direction of “emboîtement.” In a well-known note to Charles Leopold Laurillard’s Éloge, prefixed to the last edition of the Ossemens fossiles, the “radical de l’être” is much the same thing as Aristotle’s “particula genitalis” and Harvey’s “ovum.”

Bonnet’s eminent contemporary, Buffon, held nearly the same views with respect to the nature of the germ, and expresses them even more confidently.

“Ceux qui ont cru que le cœur étoit le premier formé, se sont trompés; ceux qui disent que c’est le sang se trompent aussi: tout est formé en même temps. Si l’on ne consulte que l’observation, le poulet se voit dans l’œuf avant qu’il ait été couvé.”

“J’ai ouvert une grande quantité d’œufs à differens temps avant et après l’incubation, et je me suis convaincu par mes yeux que le poulet existe en entier dans le milieu de la cicatrule au moment qu’il sort du corps de la poule.”

The “moule intérieur” of Buffon is the aggregate of elementary parts which constitute the individual, and is thus the equivalent of Bonnet’s germ, as defined in the passage cited above. But Buffon further imagined that innumerable “molécules organiques” are dispersed throughout the world, and that alimentation consists in the appropriation by the parts of an organism of those molecules which are analogous to them. Growth, therefore, was, on this hypothesis, partly a process of simple evolution, and partly of what has been termed syngenesis. Buffon’s opinion is, in fact, a sort of combination of views, essentially similar to those of Bonnet, with others, somewhat similar to those of the “Medici” whom Harvey condemns. The “molécules organiques” are physical equivalents of Leibnitz’s “monads.”

It is a striking example of the difficulty of getting people to use their own powers of investigation accurately, that this form of the doctrine of evolution should have held its ground so long; for it was thoroughly and completely exploded, not long after its enunciation, by Caspar Frederick Wolff, who in his Theoria generatìonis, published in 1759, placed the opposite theory of epigenesis upon the secure foundation of fact, from which it has never been displaced. But Wolff had no immediate